NT4 is the most recently identified member of the neurotrophin family. The need to quantify this factor is becoming apparent due to the realization of its contribution to the function of several neuronal populations within the central and peripheral nervous system e.g. preventing embryonic and postnatal motor neuron death. An efficient and sensitive method for quantification of NT4 will enhance the understanding of the physiology of NT4, as well as its involvement in disease by the estimation of NT4 in samples.